The reported growth in house dust mite populations associated with domestic environments in Europe, the Americas, China and elsewhere is causing increasing concern. With the rising number of homes remaining at a constant favourable temperature and humidity, together with changes in house cleaning methods and types of bedding over the years, the numbers and survival of such creatures have risen sharply. House dust mites are scavengers on dead organic matter found in abundance in the home, feeding principally on the shed skin scales of humans. The mites, their faeces and products, are highly antigenic as contact or aero allergens in atopic diseases, e.g. eczema, asthma and allergic rhinitis. Mite allergy may trigger severe exacerbation that can be life-threatening in extrinsic asthma.
In addition, house dust mites have, in recent years, become an increased focus of concern as many experts consider them to be instrumental in initiating primary sensitisation leading to clinical asthma in very young children. It is believed that repeated exposure to the allergens produced by the mites can trigger early stages of asthma which will then become established as a chronic disease affected by a large range of different allergens in the environment.
There is also an overwhelming body of evidence that the presence of house dust mite faeces is instrumental in provoking asthma attacks in those with asthma or specific allergies, which cause immeasurable suffering, or even death.
House dust mites are to be found concentrated in many parts of the home, particularly soft furnishing, which provide them with a highly suitable environment. When they live in bedding, however, this brings them into the closest and most prolonged contact with humans. Pillows, duvets and mattresses have been found not only to house large populations of house dust mites, but also copious amounts of their faeces. The infestation cannot generally be removed by standard cleaning methods. The faecal pellets are particularly stable and resistant to removal from the fabric.
House dust mites are members of the family acaria, and one approach which could be contemplated to reduce the population of house dust mite would clearly be the use of an acaricide. However, in a domestic environment, this would cause many problems. For example, a well-known and highly effective acaricide is benzyl benzoate, but this is known to be very toxic to cats.
An alternative acaricide would be an organophosphate compound, some of which are well-know to be highly effective in eradicating mite infestation, particularly in farm animals. However, many such organophosphate compounds are toxic to humans and suspected, even at small exposures, to promote nervous system damage over the long term. Their use in domestic situations is accordingly not recommended.
In terms of the physical means used to reduce dust mite populations, one approach which has been suggested as acceptable in a domestic environment is that of using a dusting power containing suitable acaricide, and preparations have been made available commercially for this purpose, including some containing, as the acaricidal agent, pyrethroid compounds. These are know to be relatively non-toxic to humans, and have been much promoted, especially in domestic horticulture, as "natural insecticides". some (not all) display acaricidal properties as well as insecticidal ones. However, the use of dusting powder does not provide prolonged protection against infestation, and depends particularly on the efficiency of "dusting". In addition, the powder particles themselves may aggravate any asthmatic conditions which people coming into contact with them may have.
Control of insects in domestic environments has long been practised using impregnated textiles. Insecticide-impregnated netting has been used for decades as "mosquito netting", with a view of preventing the spread of malaria and other insect vector borne diseases, not only by denying the insect physical access to the human body, but additionally by killing insects on contact with the insecticide in the netting. Such an approach clearly does nothing to reduce infestation already present in beds and soft furnishings.
A suggestion has been made to incorporate into the fibres used to make synthetic fibre netting a mite-proofing component (Fumiyasu, Japanese Patent Publication 3-220102 published Sep. 27, 1991). However, this approach traps the component within the body of each fibre and although it will have an effect, it will be attenuated, not least because the active acaricidal component will only be released by slow vaporisation, and at very low (and thus ineffective) concentration.